[PATCH v2 4/6] KVM: selftests: Add string formatting options to ucall

[Aaron Lewis <aaronlewis@google.com>]

Add more flexibility to guest debugging and testing by adding
GUEST_PRINTF() and GUEST_ASSERT_FMT() to the ucall framework.

A buffer to hold the formatted string was added to the ucall struct.
That allows the guest/host to avoid the problem of passing an
arbitrary number of parameters between themselves when resolving the
string.  Instead, the string is resolved in the guest then passed
back to the host to be logged.

The formatted buffer is set to 1024 bytes which increases the size
of the ucall struct.  As a result, this will increase the number of
pages requested for the guest.

The buffer size was chosen to accommodate most use cases, and based on
similar usage.  E.g. printf() uses the same size buffer in
arch/x86/boot/printf.c.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
---
 .../selftests/kvm/include/ucall_common.h       | 18 ++++++++++++++++++
 tools/testing/selftests/kvm/lib/ucall_common.c | 18 ++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/ucall_common.h b/tools/testing/selftests/kvm/include/ucall_common.h
index bcbb362aa77f..7281a6892779 100644
--- a/tools/testing/selftests/kvm/include/ucall_common.h
+++ b/tools/testing/selftests/kvm/include/ucall_common.h
@@ -13,15 +13,18 @@ enum {
 	UCALL_NONE,
 	UCALL_SYNC,
 	UCALL_ABORT,
+	UCALL_PRINTF,
 	UCALL_DONE,
 	UCALL_UNHANDLED,
 };
 
 #define UCALL_MAX_ARGS 7
+#define UCALL_BUFFER_LEN 1024
 
 struct ucall {
 	uint64_t cmd;
 	uint64_t args[UCALL_MAX_ARGS];
+	char buffer[UCALL_BUFFER_LEN];
 
 	/* Host virtual address of this struct. */
 	struct ucall *hva;
@@ -32,6 +35,7 @@ void ucall_arch_do_ucall(vm_vaddr_t uc);
 void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu);
 
 void ucall(uint64_t cmd, int nargs, ...);
+void ucall_fmt(uint64_t cmd, const char *fmt, ...);
 uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc);
 void ucall_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa);
 int ucall_nr_pages_required(uint64_t page_size);
@@ -47,6 +51,7 @@ int ucall_nr_pages_required(uint64_t page_size);
 #define GUEST_SYNC_ARGS(stage, arg1, arg2, arg3, arg4)	\
 				ucall(UCALL_SYNC, 6, "hello", stage, arg1, arg2, arg3, arg4)
 #define GUEST_SYNC(stage)	ucall(UCALL_SYNC, 2, "hello", stage)
+#define GUEST_PRINTF(_fmt, _args...) ucall_fmt(UCALL_PRINTF, _fmt, ##_args)
 #define GUEST_DONE()		ucall(UCALL_DONE, 0)
 
 enum guest_assert_builtin_args {
@@ -56,6 +61,17 @@ enum guest_assert_builtin_args {
 	GUEST_ASSERT_BUILTIN_NARGS
 };
 
+#define __GUEST_ASSERT_FMT(_condition, _condstr, _fmt, _args...)		  \
+do {										  \
+	if (!(_condition))							  \
+		ucall_fmt(UCALL_ABORT,						  \
+			  "Failed guest assert: " _condstr " at %s:%ld\n  " _fmt, \
+			  , __FILE__, __LINE__, ##_args);			  \
+} while (0)
+
+#define GUEST_ASSERT_FMT(_condition, _fmt, _args...)	\
+	__GUEST_ASSERT_FMT(_condition, #_condition, _fmt, ##_args)
+
 #define __GUEST_ASSERT(_condition, _condstr, _nargs, _args...)		\
 do {									\
 	if (!(_condition))						\
@@ -81,6 +97,8 @@ do {									\
 
 #define GUEST_ASSERT_EQ(a, b) __GUEST_ASSERT((a) == (b), #a " == " #b, 2, a, b)
 
+#define REPORT_GUEST_ASSERT_FMT(_ucall) TEST_FAIL("%s", _ucall.buffer)
+
 #define __REPORT_GUEST_ASSERT(_ucall, fmt, _args...)			\
 	TEST_FAIL("%s at %s:%ld\n" fmt,					\
 		  (const char *)(_ucall).args[GUEST_ERROR_STRING],	\
diff --git a/tools/testing/selftests/kvm/lib/ucall_common.c b/tools/testing/selftests/kvm/lib/ucall_common.c
index 77ada362273d..c09e57c8ef77 100644
--- a/tools/testing/selftests/kvm/lib/ucall_common.c
+++ b/tools/testing/selftests/kvm/lib/ucall_common.c
@@ -55,6 +55,7 @@ static struct ucall *ucall_alloc(void)
 		if (!test_and_set_bit(i, ucall_pool->in_use)) {
 			uc = &ucall_pool->ucalls[i];
 			memset(uc->args, 0, sizeof(uc->args));
+			memset(uc->buffer, 0, sizeof(uc->buffer));
 			return uc;
 		}
 	}
@@ -75,6 +76,23 @@ static void ucall_free(struct ucall *uc)
 	clear_bit(uc - ucall_pool->ucalls, ucall_pool->in_use);
 }
 
+void ucall_fmt(uint64_t cmd, const char *fmt, ...)
+{
+	struct ucall *uc;
+	va_list va;
+
+	uc = ucall_alloc();
+	uc->cmd = cmd;
+
+	va_start(va, fmt);
+	kvm_vsnprintf(uc->buffer, UCALL_BUFFER_LEN, fmt, va);
+	va_end(va);
+
+	ucall_arch_do_ucall((vm_vaddr_t)uc->hva);
+
+	ucall_free(uc);
+}
+
 void ucall(uint64_t cmd, int nargs, ...)
 {
 	struct ucall *uc;
-- 
2.40.0.634.g4ca3ef3211-goog